Monosodium Glutamate (MSG) Renders Alkalinizing Properties and Its Urinary Metabolic Markers of MSG Consumption in Rats

Abstract

Monosodium glutamate (MSG) is widely used as a flavor enhancer and its effects on human health are still debated. We aimed to investigate whether MSG can act as alkalinizing agent in murine models and if its metabolites are biomarkers of MSG consumption. For this purpose, adult male Wistar rats were given water added with 1 g% MSG or three types of control water, including sodium chloride (NaCl) and sodium bicarbonate (NaHCO₃). At 14 days, urinary pH, electrolytes, urinary metabolites and ion-exchanger gene expression were determined. The results revealed that MSG-treated rats had significantly more alkaline urine and higher levels of urinary sodium and bicarbonate similar to NaHCO₃ controls. These changes correlated with a lower expression of ion-exchanger genes, namely, CAII, NBC1, and AE1, which are involved in bicarbonate kidney reabsorption. The urinary metabolic profiles also revealed similar patterns for the MSG and NaHCO₃ groups. In conclusion, MSG exhibits similar properties to NaHCO₃, an alkalinizing agent, with regard to inducing alkaline urine, reducing bicarbonate kidney reabsorption, and generating a specific urinary metabolic pattern. We believe that these observations will be useful to further study the MSG effects in humans.

Keywords: alkaline urine; ion exchangers; metabolic profiles; monosodium glutamate.

Figure 1

A schematic diagram showing the experimental design and sample collection.

Figure 2

Urine pH (A) and electrolytes (B) after treatment in male Wistar rats supplemented with 1 g% MSG, 0.34 g% NaCl and 2.4 g% NaHCO₃ (n = 10 per group). Data are shown as mean ± SEM and p-values calculated by Student’s t-test (* p < 0.05, ** p < 0.01, *** p < 0.001).

Figure 3

Changes in mRNA expression of ion exchanger genes in cortex layers of rat kidney after 14 days of MSG (n = 10), NaCl (n = 10) and NaHCO₃ (n = 10) supplementation compared to controls (n = 8) (A) CAII, (B) NBC1, (C) AE1. Data are shown as mean ± SEM relative gene expression with beta-actin, * p < 0.05; ** p < 0.01; *** p < 0.001. Abbreviations: CAII: carbonic anhydrase2, NBC1: Na⁺-HCO₃⁻ co-transporter1; AE1: anion exchanger1.

Figure 4

The 600 MHz ¹H-NMR spectra of urinary samples collected over 24 h at day 14 from (A) control, (B) MSG-fed, (C) NaCl-fed, and (D) NaHCO₃ –fed rats (n = 10 per group).

Figure 5

PCA scores plots (left panel) and O-PLS-DA cross-validated scores plots (right panel) of 24-h urine at day 14 (U24 D14). (A,B): control (blue) vs. MSG (red); (C,D): control (blue) vs. NaCl (green); (E,F): control (blue) vs. NaHCO₃ (brown) (n = 10 per group).